Because it makes sense.

They tend to do it first thing in the morning to prepare them to be at their best.

They are proactive and not reactive.

You are what you repeatedly do every single day, so if you include a morning ritual you are likely to help yourself on your way to become more successful - whatever success means to you.

Tony Robbins meditates and calls it his "hour to power". He does a number of other things but as someone who has interviewed many of the most powerful people on the planet, he knows what makes sense.

If you think that you might not have the time or know what to do, you're not alone.  But to find out what to do all you have to do is a quick online search to find a method that suits you.

If it will help, I can recommend www.Mindstore.com 

You can also get really good books on meditation.